Data from GeoJSON URL end point not appearing on Map using MKAnnotations - ios

Question

I am creating my first IOS app and am not a developer and am really stuck with Map Annotations.
I am trying to get Fire data from a GeoJSON URL end point and display the fires as Annotations on a Map using URLSession and a custom MKAnnotationView and custom fire Pins.
The problem is the Annotations with the GeoJSON Fire data from the URL end point are not appearing on the Map, although data is being returned by the URL session. However, if I manually create a single Fire annotation it is appearing correctly on the map with the custom pin.
Any help would be immensely appreciated, I have spent days trying to figure this out :(
Here is the ViewController.Swift file
import UIKit
import MapKit
import CoreLocation
class ViewController: UIViewController, CLLocationManagerDelegate, MKMapViewDelegate {
#IBOutlet weak var mapView: MKMapView!
var locationManager:CLLocationManager!
var lat = Double()
var lon = Double()
var fires: [Fire] = []
override func viewDidLoad() {
super.viewDidLoad()
mapView.delegate = self
mapView.register(FireMarkerView.self,forAnnotationViewWithReuseIdentifier:
MKMapViewDefaultAnnotationViewReuseIdentifier)
if let url = URL(string: "https://services3.arcgis.com/T4QMspbfLg3qTGWY/arcgis/rest/services/Active_Fires/FeatureServer/0/query?outFields=*&where=1%3D1&f=geojson") {
URLSession.shared.dataTask(with: url) {data, response, error in
if let data = data {
do {
let features = try MKGeoJSONDecoder().decode(data)
.compactMap { $0 as? MKGeoJSONFeature }
let validWorks = features.compactMap(Fire.init)
self.fires.append(contentsOf: validWorks)
print([self.fires])
}
catch let error {
print(error)
}
}
}.resume()
}
//This code works an annotation appears correctly on map
/* let fire = Fire(
title: "Ford Fire",
incidentShortDescription: "Hwy 35",
incidentTypeCategory: "WF",
coordinate: CLLocationCoordinate2D(latitude: 37.7993, longitude: -122.1947))
mapView.addAnnotation(fire)*/
mapView.addAnnotations(fires)
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
determineMyCurrentLocation()
}
func locationManagerDidChangeAuthorization(_ manager: CLLocationManager) {
switch manager.authorizationStatus {
case .authorizedAlways , .authorizedWhenInUse:
mapView.showsUserLocation = true
followUserLocation()
locationManager.startUpdatingLocation()
break
case .notDetermined , .denied , .restricted:
locationManager.requestWhenInUseAuthorization()
break
default:
break
}
switch manager.accuracyAuthorization {
case .fullAccuracy:
break
case .reducedAccuracy:
break
default:
break
}
}
func followUserLocation() {
if let location = locationManager.location?.coordinate {
let region = MKCoordinateRegion.init(center: location, latitudinalMeters: 4000, longitudinalMeters: 4000)
mapView.setRegion(region, animated: true)
}
}
func determineMyCurrentLocation() {
locationManager = CLLocationManager()
locationManager.delegate = self
locationManager.desiredAccuracy = kCLLocationAccuracyBest
locationManager.requestAlwaysAuthorization()
if CLLocationManager.locationServicesEnabled() {
locationManager.startUpdatingLocation()
//locationManager.startUpdatingHeading()
}
}
func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
guard let location = locations.last else { return }
let userLocation = locations.first! as CLLocation
lat = userLocation.coordinate.latitude
lon = userLocation.coordinate.longitude
let region = MKCoordinateRegion.init(center: location.coordinate, latitudinalMeters: 400000, longitudinalMeters: 400000)
self.mapView.setRegion(region, animated: true)
// Call stopUpdatingLocation() to stop listening for location updates,
// other wise this function will be called every time when user location changes.
// Need a solution for this.
manager.stopUpdatingLocation()
print("user latitude = \(userLocation.coordinate.latitude)")
print("user longitude = \(userLocation.coordinate.longitude)")
}
func locationManager(_ manager: CLLocationManager, didFailWithError error: Error)
{
print("Error \(error)")
}
}
Here is the Model Class, Fire.swift
import Foundation
import MapKit
class Fire: NSObject, MKAnnotation {
let title: String?
let incidentShortDescription: String?
let incidentTypeCategory: String?
let coordinate: CLLocationCoordinate2D
init(
title: String?,
incidentShortDescription: String?,
incidentTypeCategory: String?,
coordinate: CLLocationCoordinate2D
) {
self.title = title
self.incidentShortDescription = incidentShortDescription
self.incidentTypeCategory = incidentTypeCategory
self.coordinate = coordinate
super.init()
}
init?(feature: MKGeoJSONFeature) {
// 1
guard
let point = feature.geometry.first as? MKPointAnnotation,
let propertiesData = feature.properties,
let json = try? JSONSerialization.jsonObject(with: propertiesData),
let properties = json as? [String: Any]
else {
return nil
}
// 3
title = properties ["IncidentName"] as? String
incidentShortDescription = properties["IncidentShortDescription"] as? String
incidentTypeCategory = properties["IncidentTypeCategory"] as? String
coordinate = point.coordinate
super.init()
}
var subtitle: String? {
return (incidentTypeCategory)
}
var image: UIImage {
guard let name = incidentTypeCategory else {
return #imageLiteral(resourceName: "RedFlame")
}
switch name {
case "RX":
return #imageLiteral(resourceName: "YellowFlame")
default:
return #imageLiteral(resourceName: "RedFlame")
}
}
Here is the custom MKAnnotation Class: FileMarkerView.swift
import Foundation
import MapKit
class FireMarkerView: MKAnnotationView {
override var annotation: MKAnnotation? {
willSet {
guard let fire = newValue as? Fire else {
return
}
canShowCallout = true
calloutOffset = CGPoint(x: -5, y: 5)
rightCalloutAccessoryView = UIButton(type: .detailDisclosure)
image = fire.image
}
}
}

Answer 1

URLSession.shared.dataTask is an asynchronous task, meaning it calls its callback function at some indeterminate time in the future. Code executed outside of its callback (the { }) will end up getting called before the data task has actually completed. Right now, you're setting the annotations outside of that callback.
To solve this, you need to set the annotations inside of that callback function. So, where you have print([self.fires]), you can do:
DispatchQueue.main.async {
self.mapView.addAnnotations(self.fires)
}
The DispatchQueue.main.async is to make sure that an update to the UI gets called on the main thread (the URL task may return on a different thread).